1. Field of the Invention
The present invention relates to a coding apparatus including an arithmetic coding medium for use in a facsimile device, an image storing apparatus, and the like. In particular, the present invention relates to a coding apparatus capable of securing the confidentiality of transmitted image information, and an information processing apparatus provided with the coding apparatus.
2. Discussion of the Background Art
There are background systems for confidentially transmitting information, for example with a facsimile machine. If the contents of information have to be made confidential for a third party at the time of communicating binary-value image data, in one system only a person capable of inputting a password in a confidential personal communication mode can usually output the data, for instance, in a facsimile device. Or otherwise, in consideration of the communication being intercepted or monitored by the third party, the image can be scrambled, i.e. encrypted, and thereby the output image cannot be discriminated without being decrypted. However, if high confidentiality is required to be obtained, the scrambling algorithm becomes complicated. As a result, the speed of processing may be lowered. The above-mentioned matter of the background art is a problem to be solved.
The communication apparatus as disclosed in the published specification of Japanese Laid-open patent publication No. 8-107,506/1996 has already provided a confidentiality technology relating to a progressive mode among the JBIG (Joint Bi-level Image Experts Group) system prescribed in JISX4311: ISO/IEC11544 which is an international standard of the binary-image coding method. The progressive mode is a coding method of stepwisely restoring an image at a time of decoding the image from a low-resolution image to a high-resolution image. However, in order to solve the above-mentioned problems, an encryption processing is practiced only for the lowest-resolution layer in the JBIG system.
When the image of a one-step higher resolution is restored, unless the encrypted layer of the lowest resolution is changed to a plain text or descrambled or decrypted by adopting the method of referring to the restored image on the layer of the one-step lower resolution, the image of the one-step higher resolution layer cannot be restored.
As to the tier type coding method of the binary image, the JBIG algorithm is further described. As seen in the rapidly and widely spread popularization of the facsimile device etc., almost all parts of a business document include binary-value information of black-and-white. Regarding the methods of effectively coding such binary-value information, the methods of Modified Huffman (MH), Modified READ (Relative Element Address Designate) (MR), and Modified-Modified READ (MMR) have already been standardized, and practically applied to G3 and G4 facsimile devices.
Such coding methods are established by estimating the hard copy represented, for instance, by the facsimile device. The methods are premised on the so-called sequential build-up of scanning the paper document surface from left to right and from top to bottom and performing the coding operation in the above order. According to these methods, at the receiving side, the received information can be decoded without storing any information recorded on the paper surface immediately. For this reason, such methods can be suitably adopted to a facsimile device.
On the other hand, in addition to the diversification of the image communication, there has been further proposed a progressive build-up which is capable of promptly transmitting an entire image even in the case of a rough or poor image quality, and which is further capable of adding additional image information as occasion demands, and thereby improving the image quality.
In the case of restoring the image of one-step higher resolution, a one-grade higher resolution layer cannot be restored if the encrypted lowest-resolution layer cannot be decrypted, by adopting the method of referring to the restoring image of the one-step-lower resolution.
Heretofore, the background art regarding the communication apparatus is described. However, according to such background art which is disclosed in the background-art documents, e.g., the published specification of Japanese Laid-open Patent Publication No. 8-107,506/1996, and other relevant documents, etc., there exists no advantageous functional effect.
To state in more detail, the published specification of Japanese Patent Publication No. 8-107,506 regarding a communication apparatus describes a method of maintaining confidentiality with respect to the progressive mode (the coding method of stepwisely restoring the image from the low resolution to the high resolution at the time of decoding) among the JBIG (Joint Bi-level Image experts Group) method (JISX4311:ISO/IEC11544) which is an international standard of the binary image coding method.
In the above-mentioned communication apparatus, the encryption processing is executed for the lowest-resolution layer in the JBIG method. At the time of decoding, the processing is advanced referring to the restored image of the lowest-resolution layer, and the image of the one-step higher resolution is restored. Therefore, if the lowest-resolution layer is encrypted, the next-stage resolution layer cannot be correctly decoded unless the cryptogram is changed to a plaintext, namely, decrypted.
Furthermore, as to the high-resolution layer of the subsequent stage, the resolution of the preceding stage image is referenced. Consequently, if the preceding stage image cannot be decrypted, it turns out to become impossible to correctly reproduce the image in the processing performed thereafter. In such a way, the confidentiality of the image can be accomplished.
For instance, when the JBIG method is employed in the facsimile device, a sequential mode (the mode of reproducing the image in order from the top to the bottom side at the time of decoding) is used instead of the aforementioned progressive mode.
On this occasion, since the image is not constructed with such a tier-type image structure, the entire area of the data after coding becomes the object to be encrypted. For this reason, if the amount of the data to be coded is too much, the time required for processing of changing the cryptogram to the plaintext and vice versa (encrypting and decrypting) is also increased on some occasions. Furthermore, the above-mentioned background art document Japanese Laid-open Patent Publication No. 8-107,506 regarding the aforementioned communication apparatus does not describe at all the algorithm of performing the encrypting operation.
On the other hand, the present invention aims at providing a novel data coding apparatus capable of enhancing confidentiality with a high speed.
The present invention was made in order to solve the above-mentioned and other problems in the background art. Accordingly, it is an object of the present invention to solve the background-art defects such as noted in the above-mentioned problems.
It is another object of the present invention to provide a novel coding apparatus capable of solving the background-art defects and thereby obtaining high confidentiality.
It is still another object of the present invention to provide a novel coding apparatus capable of obtaining the functional effect of obtaining a high-speed operation even in the case of not including plural resolution layers.
It is still another object of the present invention to provide a novel information processing apparatus provided with the above-mentioned coding apparatus and further including a specified information setting medium.